MMR vaccines: do they work and are they safe?

In a blog for parents/carers, Siobhan McCormack, a Paediatric Specialist Registrar, looks at the latest Cochrane evidence on MMR vaccination and at guidance on vaccination during the current COVID-19 pandemic.

In the midst of the COVID19 pandemic, getting your child’s routine vaccinations may be the last thing on your mind, or perhaps you are wondering whether it’s ok to go to a clinic at the moment and whether it would be better to wait. Even without these unusual considerations, some parents worry about childhood vaccinations and whether they are safe.

As a children’s doctor, I was pleased to see that Cochrane have updated a review on the MMR (Measles, Mumps, Rubella) vaccine, giving us the latest evidence on its effectiveness and safety. We’ve also had advice from the World Health Organisation (WHO) about vaccination during the COVID19 pandemic. Before we look at these, a bit about why vaccines are important.

Why are vaccines important?

Vaccines prevent 2 to 3 million deaths per year worldwide currently and have potential to prevent a further 1.5 million with increased availability and uptake (WHO 2019). Vaccine coverage around the world is suboptimal, in part due to lack of vaccine knowledge and confidence. Attitudes towards vaccination including negative perceptions of efficacy and safety are potential barriers to effective vaccination strategies.

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Vaccines prevent 2 to 3 million deaths per year worldwide.

Measles, mumps and rubella (German measles) are contagious viral illnesses, most commonly seen in children and young people. Two doses of the MMR vaccine are part of the NHS vaccination schedule.  These viruses can potentially lead to serious infections resulting in long-term disability or death. Worldwide, measles accounts for one of the largest causes of death in children. The UK has lost its measles-free status and measles outbreaks have been reported across Europe and the United States in recent years in areas where vaccine coverage has been low. Mumps cases soared in England in 2019 with a five-fold increase from the previous year. Most outbreaks have been in colleges and universities, prompting a campaign to encourage young people to get vaccinated, with Public Health England advising that it is never too late for catch-up vaccination if there is any doubt.

What is the guidance on routine vaccinations in the COVID-19 pandemic?

In the midst of the COVID-19 pandemic, other vaccine-preventable illnesses do not disappear, but rather can pose an increased threat if vaccination rates in the population are not maintained. Even small declines in uptake can have a massive impact for highly infectious diseases such as measles. Children’s charity Unicef has voiced concerns that pausing routine schedules could increase numbers of children at risk, cause undue pressure on already stretched health services, and even have potential to cause a further pandemic of other contagious, vaccine preventable illnesses.

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The World Health Organization (WHO) issued guidance in March 2020 emphasising the importance of routine vaccination during the COVID-19 pandemic.

The World Health Organization (WHO) issued guidance in March 2020 emphasising the importance of routine vaccination and advocating that routine sessions be maintained, and this was also endorsed by Public Health England and the Irish Health Service Executive. In the case where this cannot be facilitated, the children affected should be prioritised for catch-up planning as soon as possible. Healthcare providers have been given guidance on measures to take to limit the transmission of the virus during vaccination encounters. 

What did the Cochrane Review find?

A Cochrane Review was updated in April 2020 to include the latest evidence on whether MMR vaccines are safe and effective at preventing these illnesses in children. They also looked at the varicella (chicken pox) vaccine, which in some countries is given with the MMR vaccine but is not part of the routine schedule in the UK and Ireland.

Evidence on how well the vaccines work

The studies of how well the vaccines work examined 10 million children across 51 studies. The review authors judged the certainty of the evidence and found it to be ‘moderate’ for the MMR vaccine and high for the varicella vaccine.

Complete MMR courses were reported to be:

  • 96% effective at preventing measles
  • 86% effective at preventing mumps
  • 89% effective at preventing rubella

The varicella vaccine was reported to be 95% effective at preventing chicken pox.

Evidence on vaccine safety

Evidence on the safety of MMR vaccines comes from 13 million children across 87 studies.

Two studies with almost 1.2 million children, of moderate certainty evidence, found no association between MMR vaccines and autism.

Two other studies of over 1 million children found no evidence that MMR vaccines are associated with an increased risk of a number of conditions, including: asthma, hay fever, dermatitis, eczema, type 1 diabetes, inflammatory bowel disease, multiple sclerosis, leukaemia, encephalitis, cognitive delay, gait disturbance and viral or bacterial infections.

The analyses showed very small risks of fits due to high temperature or fever (febrile seizures) around two weeks after vaccination, and of a condition where blood does not clot normally (idiopathic thrombocytopenic purpura or ITP) in vaccinated children. However, febrile seizures normally occur in 2% to 4% of healthy children at least once and the risk of ITP after vaccination is smaller than after natural infection with these illnesses . 

What does this mean?

Moderate certainty evidence found MMR vaccination for children to be effective. Moderate certainty evidence also found no evidence that MMR vaccination is associated with autism nor a number of other unwanted effects. Together, this evidence supports its use for mass immunisation.

These illnesses continue to be a threat to children’s health and increased vaccination uptake will be required to get England back to a measles-free state through this pandemic time where Unicef, the World Health Organisation and Public Health England are all advocating the maintenance of routine vaccination schedules.

If you are still concerned about vaccinating your child, a discussion with your GP or practice nurse may help. The NHS website also has a useful factsheet “Why vaccination is safe and important”.

Take home points

Take home points: A Cochrane Review has shown that MMR vaccines are effective at preventing measles, mumps, rubella in children.The review found no evidence of an increased risk of autism from MMR vaccination.World Health Organization guidance, supported by Public Health England, advises having routine vaccinations during the COVID 19 pandemic.It is never too late to catch-up on MMR vaccination.

Join in the conversation on Twitter with @siobhanmccorm  @CochraneUK or leave a comment on the blog. Please note, we will not publish comments that link to commercial sites or appear to endorse commercial products.

References (pdf).

Siobhan McCormack has nothing to disclose.


Siobhan McCormack

About Siobhan McCormack

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Dr Siobhan McCormack is a Specialist Registrar in Paediatrics in Dublin. She graduated from the National University of Ireland, Galway in 2014 and was conferred as a member of the Royal College of Physicians of Ireland in 2017. Siobhan is a member of the Cochrane UK & Ireland Trainees Advisory Group (CUKI TAG). Her research interests include general and developmental paediatrics and child public health. She has a keen interest in best practice application and quality improvement and is a member of the quality workstream for Ireland’s New Children’s Hospital. She is currently completing a Masters in Paediatrics and Child Health at the University of Brighton.

1 Comments on this post

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    Dr. McCormack has given a very nice summary in relation to the effectiveness and safety of MMR vaccination . Special credit goes to converting the evidence into a language that parents could understand and relate to.

    Prof. Roy K Philip / Reply

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